125 research outputs found
Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films
It is known that solid-state reaction in high-pressure oxygen can stabilize
high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend
this superoxygenation concept of synthesis to thin films which, due to their
large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial
thin films of grown by pulsed laser deposition are
annealed at up to 700 atm O and 900C, in conjunction with Cu
enrichment by solid-state diffusion. The films show clear formation of
and as well as regions
of and YBaCuO phases,
according to scanning transmission electron microscopy, x-ray diffraction and
x-ray absorption spectroscopy. Similarly annealed
powders show no phase conversion. Our results demonstrate a novel route of
synthesis towards discovering more complex phases of cuprates and other
superconducting oxides.Comment: Accepted for publication in Physical Review Material
Controlling the interfacial conductance in LaAlO₃/SrTiO₃ in 90∘ off-axis sputter deposition
We report on the fabrication of conducting interfaces between
LaAlO
3
and
SrTiO
3
by
90
∘
off-axis sputtering in an Ar atmosphere. At a growth pressure of 0.04 mbar the interface is metallic, with a carrier density of the order of
1
×
10
13
cm
−
2
at 3 K. By increasing the growth pressure, we observe an increase of the out-of-plane lattice constants of the
LaAlO
3
films while the in-plane lattice constants do not change. Also, the low-temperature sheet resistance increases with increasing growth pressure, leading to an insulating interface when the growth pressure reaches 0.10 mbar. We attribute the structural variations to an increase of the La/Al ratio, which also explains the transition from metallic behavior to insulating behavior of the interfaces. Our research shows that the control which is furnished by the Ar pressure makes sputtering as versatile a process as pulsed laser deposition, and emphasizes the key role of the cation stoichiometry of
LaAlO
3
in the formation of the conducting interface
Long-term dry immersion: review and prospects
Dry immersion, which is a ground-based model of prolonged conditions of microgravity, is widely used in Russia but is less well known elsewhere. Dry immersion involves immersing the subject in thermoneutral water covered with an elastic waterproof fabric. As a result, the immersed subject, who is freely suspended in the water mass, remains dry. For a relatively short duration, the model can faithfully reproduce most physiological effects of actual microgravity, including centralization of body fluids, support unloading, and hypokinesia. Unlike bed rest, dry immersion provides a unique opportunity to study the physiological effects of the lack of a supporting structure for the body (a phenomenon we call \u27supportlessness\u27). In this review, we attempt to provide a detailed description of dry immersion. The main sections of the paper discuss the changes induced by long-term dry immersion in the neuromuscular and sensorimotor systems, fluid-electrolyte regulation, the cardiovascular system, metabolism, blood and immunity, respiration, and thermoregulation. The long-term effects of dry immersion are compared with those of bed rest and actual space flight. The actual and potential uses of dry immersion are discussed in the context of fundamental studies and applications for medical support during space flight and terrestrial health care
Controlling the interfacial conductance in LaAlO3/SrTiO3 in 90^o off-axis sputter deposition
Quantum Matter and Optic
Corrigendum to “Seasonal variations of Quercus pubescens isoprene emissions from an in natura forest under drought stress and sensitivity to futureclimate change in the Mediterranean area”
International audienc
Coupling charge and topological reconstructions at polar oxide interfaces
In oxide heterostructures, different materials are integrated into a single
artificial crystal, resulting in a breaking of inversion-symmetry across the
heterointerfaces. A notable example is the interface between polar and
non-polar materials, where valence discontinuities lead to otherwise
inaccessible charge and spin states. This approach paved the way to the
discovery of numerous unconventional properties absent in the bulk
constituents. However, control of the geometric structure of the electronic
wavefunctions in correlated oxides remains an open challenge. Here, we create
heterostructures consisting of ultrathin SrRuO, an itinerant ferromagnet
hosting momentum-space sources of Berry curvature, and LaAlO, a polar
wide-bandgap insulator. Transmission electron microscopy reveals an atomically
sharp LaO/RuO/SrO interface configuration, leading to excess charge being
pinned near the LaAlO/SrRuO interface. We demonstrate through
magneto-optical characterization, theoretical calculations and transport
measurements that the real-space charge reconstruction modifies the
momentum-space Berry curvature in SrRuO, driving a reorganization of the
topological charges in the band structure. Our results illustrate how the
topological and magnetic features of oxides can be manipulated by engineering
charge discontinuities at oxide interfaces.Comment: 5 pages main text (4 figures), 29 pages of supplementary informatio
Co valence transformation in isopolar LaCo O<sub>3</sub>/LaTi O<sub>3</sub> perovskite heterostructures via interfacial engineering
Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth
The two-dimensional electron gas occurring between the band insulators SrTiO3
and LaAlO3
continues to attract considerable interest, due to the possibility of dynamic control over the carrier density and due to ensuing phenomena such as magnetism and superconductivity. The formation of this conducting interface is sensitive to the growth conditions, but despite numerous investigations there are still questions about the details of the physics involved. In particular, not much is known about the electronic structure of the growing LaAlO3
layer at the growth temperature (around 800∘C
) in oxygen (pressure around 5×10−5
mbar), since analysis techniques at these conditions are not readily available. We developed a pulsed laser deposition system inside a low-energy electron microscope in order to study this issue. The setup allows for layer-by-layer growth control and in situ measurements of the angle-dependent electron reflection intensity, which can be used as a fingerprint of the electronic structure of the surface layers during growth. By using different substrate terminations and growth conditions we observe two families of reflectivity maps, which we can connect either to samples with an AlO2
-rich surface and a conducting interface or to samples with a LaO-rich surface and an insulating interface. Our observations emphasize that substrate termination and stoichiometry determine the electronic structure of the growing layer, and thereby the conductance of the interface.Quantum Matter and Optic
- …